American Express has also turned its transaction data into a revenue stream through its Business Insights consulting division which has aimed direct mail and online offers to card holders on behalf of advertisers for years, though on an aggregate level. More recently, AmEx has modeled audience segments for use in online ad targeting. The company declined to name any partners in the endeavor, but stressed the AmEx data models don't allow for direct targeting of its card holders.

Mastercard recently aligned with Maxpoint, a digital-ad firm that combines lots of publicly available information, such as data from Secretaries of State and health data from the Centers for Disease Control, to define audiences within specific ZIP code regions. The Mastercard information is "the first credit-card data set that we've incorporated into our system," said Maxpoint CEO Joe Epperson.

Maxpoint sells display, mobile and video ads featuring targeted coupons or store promotions on behalf of CPG brands and other types of advertisers such as restaurants. The Mastercard data shows how high or low people index within a specific ZIP code for certain types of purchases. Using the Mastercard data, a burger or pizza chain might use the system to push promotions to neighborhoods in which people spend more than the average at fast-food joints. The firms have worked together for around six months to get the system in place.

Mastercard also makes its data available through Exelate, a data-management platform that feeds information from Mastercard and other partners including Acxiom and Nielsen into digital-ad exchanges for targeting. The credit-card firm compiles audience segments based on its cardholders' transactions, pegging people as likely to shop at a sporting goods store or specialty retailer, for example. Exelate uses another company to transfer the Mastercard segments online to target large, modeled audiences geographically according to ZIP+4 codes, rather than targeting individuals based on their personal transactions.

Mastercard stresses the transaction data is anonymized and provided in aggregate. "It's really more of a broad database," said Susan Grossman, group head of media solutions for MasterCard Advisors Information Services.

Privacy Qualms
Advertisers can target ads to large pools of Mastercard customers categorized into segments such as "Top Tier Auto Spenders," or "Frequent Transactors," said a source at a media-agency trading desk using Mastercard data who asked to remain anonymous. The information is "not very granular," said the source, who suggested privacy concerns have prevented Mastercard from offering more detailed data on an individual basis.

Still, the source indicated he thought he was targeting actual Mastercard cardholders through online matching and cookie dropping, rather than merely targeting geographic-level segments. While he said the Mastercard data performs relatively better than other information available for digital targeting, the source called it "convoluted."

Privacy concerns certainly play a role in how firms like Mastercard make their data available, but those qualms aren't preventing purchase data from seeping online more frequently. Acxiom has partnered with Facebook to test ad targeting on the social site using customer loyalty shopping data. The company also recently unveiled plans to connect the data it stores for its clients including purchase history and loyalty card information to publisher sites.

Venture Development Center serves as an intermediary between data brokers and brands and data providers. The company has discussed data monetization with most if not all credit card firms, said VDC President and COO Matthew Staudt, noting they have "a high level of interest, but also a very strong sense of caution."

The information supplied by credit card firms and other data companies like Acxiom is arguably more reliable because it reflects real consumer purchases as opposed to inferences about what people appear to be interested in. The majority of behavioral data used to target digital ads has its share of problems, suggested the trading desk source who said people might be added to audience segments (think in-market shoe buyers) based only on a one-time site visit. In addition, some computers in homes are used by multiple people, muddying behavioral profiles.